Examples of conventional air bag devices include an air bag device for protecting a driver of a vehicle from a shock resulting from a collision or the like, wherein the air bag device is incorporated in the boss portion of the steering wheel of the vehicle. This air bag device is provided with an inflator for ejecting gas, a pouch-shaped air bag stored in a folded state, a cover for covering the air bag, and a base plate to which the inflator, the air bag and the cover are attached. When the air bag device having a structure as above detects a shock which may result from a collision of the vehicle, in other words when it detects sudden deceleration that exceeds a given speed reduction rate, the device ejects gas from the inflator, so that the pressure resulting from the expansion of the air bag tears the cover along a predetermined tear line and opens the cover like doors, thereby projecting the air bag from the cover and unfolding and inflating the air bag in front of the driver. In order to appropriately receive the driver and effectively absorb a shock delivered to his head and abdomen regardless of his physical features, which may vary depending on occupants, or driving postures or other seating positions, it is desired that the air bag has such inflation characteristics that the distance by which the air bag projects towards the front of the driver is limited to an extent just sufficient to receive the upper part of the body of the driver who is leaning forward and that the air bag is extended rapidly to a sufficient extent in radial directions.
An example of structures dealing with the above problems is disclosed in Japanese Patent Laid-open No. 224438-1992, which calls for attaching a catching belt to the inner surface of the side of the air bag facing the driver and connecting the belt to the container of the air bag. However, the above structure complicates the production process of the air bag device, because it requires an operation for attaching an end of the catching belt to the inner side of the air bag and another operation, when the air bag device is assembled, for attaching the other end of the catching belt to a specified portion of the container of the air bag, said portion of the container located further inside the device. In addition, it presents another problem in that the air bag tends to become excessively bulky when folded in the state where the catching belt is disposed in the air bag.
Another example of air bag devices is disclosed in Japanese Patent laid-open No. 104196-1996, which calls for providing another bag material inside the air bag and sewing one of the bag materials that constitute the air bag to said inner bag material in such a manner that a part of the bag material can be torn. However, as this configuration requires an additional bag material to be provided inside the bag materials that constitute the air bag, it complicates the sewing process. An air bag is formed into a bag usually by sewing together two bag materials along the edge and then turning the sewed materials inside out. According to the above configuration, however, the additional inner bag material is so disposed as to connect each one of two outer bag materials to the other. In other words, the process of sewing the inner bag material is a separate step from the step for sewing together the base bag materials. Therefore, said configuration presents a problem in that steps of machine sewing are increased.
As described above, the configuration which calls for disposing a catching belt in an air bag and connecting the belt to the container of the air bag presents such drawbacks as to make the production process complicated and increase the volume of the air bag in the folded state. The configuration which calls for disposing an additional bag material in an air bag and sewing a bag material of the air bag to the inner bag material in such a manner that a part of the bag material can be torn has drawbacks in that the sewing process of the air bag becomes complicated, because another bag material has to be provided inside the bag materials that constitute the air bag.
In order to solve the above problems, an object of the present invention is to provide an air bag device which is easy to be produced and has superior performance characteristics for inflating the air bag.